1. Field of the Invention
The present invention relates to an image forming apparatus such as an apparatus of the electrophotographic type, for example, a copier, a printer, or a facsimile apparatus, and particularly to a belt cartridge attaching and detaching mechanism for accommodating and replacing a belt. The belt which is to be replaced includes: a photosensitive belt on which an electrostatic latent image is to be formed; an intermediate transfer belt which once retains a toner image formed on a photosensitive member and then transfers the image onto a transfer member; and a transfer medium transport belt which transports such a transfer member.
2. Description of the Related Art
In an image forming apparatus of the electrophotographic type such as a copier, a printer, or a facsimile apparatus, an electrostatic latent image is written in the surface of a drum-like or belt-like photosensitive member which is uniformly charged, and the electrostatic latent image is developed by a toner. The toner image on the photosensitive member is directly transferred to a transfer medium such as a copy sheet, or the toner image on the photosensitive member is primary-transferred to an intermediate transfer belt and the transferred toner image is secondary-transferred to a transfer medium, so that a so-called hard copy of an image is obtained.
In such an image forming apparatus, the photosensitive belt, the intermediate transfer belt, and the transfer medium transport belt are worn in accordance with the use condition and deterioration with time, and therefore must be periodically replaced with a new one.
JP-A-8-123294 discloses a method wherein shafts between which a belt is stretched are movably configured so that replacement of the belt only can be performed.
It is known that, when the peripheral lengths of the ends in the width direction perpendicular to the transportation direction of the belt are different from each other or tensions are varied, the belt meanders. It is difficult to produce a belt so that the peripheral lengths of the ends in the width direction are equal to each other, and to balance tensions of the lateral or right and left sides with each other. Therefore, a mechanism in which the lateral ends of rollers are enabled to be moved in any direction, and a spring is attached to each of the ends so as to make proper the tensions of the right and left sides of the belt, or which corrects meandering is required.
JP-A-57-60356 discloses a method in which a restricting member is disposed in the vicinity of an end of a roller to prevent a belt from meandering. When the belt meanders in a larger degree, however, the belt rides over a stopper so that the belt is wrinkled or the belt itself is damaged.
JP-A-4-133926 discloses a method in which a tapered ring is coupled with the shaft of a steering roller, and the steering roller is tilted in accordance with a force which is produced by meandering of a belt to cause the tapered ring to be forcedly rotated, thereby correcting meandering.
However, it is difficult to take out only the belt from the complicated inner space of the apparatus. In attachment of a belt, the belt may be damaged. Since shafts between which the belt is stretched are moved, the parallelism between the shafts must be accurately adjusted at each replacement of a belt.
In the above-mentioned structures of the conventional art, when a disposal belt cartridge is used, also many gears and clutches which are disposed in the belt cartridge are replaced and junked together with other components. This is very uneconomical from the viewpoints of saving of resources and the cost. Therefore, the structures are not suitable for the disposal type. Also in the case of a recycling belt cartridge, a prolong time period is required for recycling and checking because of the complicated structure of the belt cartridge. Therefore, the structures are not suitable also for the recycling type.
When the degree of meandering is changed during operation or the ability of correcting meandering becomes in sufficient owing to deterioration with time, meandering of a belt cannot be sometimes completely corrected.
It is an object of the invention to provide an image forming apparatus which is of the type wherein, in replacement of a belt, the belt is replaced together with a belt cartridge, in which the structure of the belt cartridge is simplified and the number of components is reduced, and which has a structure that, in the case of the disposal type, the amount of waste matter is reduced, and in the case of the recycling type, the time period and man power required for recycling and checking can be reduced so that the total running cost can be lowered.
It is another object of the invention to provide an image forming apparatus which is of the type wherein only a belt is replaced, and which comprises a tension applying/releasing mechanism that causes a belt tension applying mechanism and a tension roller to be engaged with and disengaged from each other.
It is a further object of the invention to provide an image forming apparatus which comprises a belt meandering correcting mechanism that accurately corrects meandering of a belt.
In order to attain the object, the invention provides an image forming apparatus in which a belt cartridge incorporating a belt and plural rolls that support the belt is detachably mounted in a main unit of the image forming apparatus to enable the belt to be replaced, wherein at least one of the plural rolls is a tension roller in which a rotation shaft is movable in a direction along which predetermined tension is applied to the belt, the belt cartridge comprises an attachment/detachment guide pin which is used in attachment to and detachment from the main unit of the image forming apparatus, the main unit of the image forming apparatus comprises a belt tension applying mechanism which moves the tension roller to apply predetermined tension to the belt, and a guide groove which is used in attachment and detachment of the belt cartridge, and in attachment of the belt cartridge, the attachment/detachment guide pin is guided by the attachment/detachment guide groove, and the belt tension applying mechanism is engaged with the rotation shaft of the tension roller to apply the predetermined tension to the belt.
In the invention, the belt tension applying mechanism which moves the tension roller to apply predetermined tension to the belt, and the guide groove which is used in attachment and detachment of the belt cartridge are disposed on the side of the main unit of the image forming apparatus. In the case where the belt cartridge is of the disposal type, therefore, it is not required to dispose many gears and clutches in the belt cartridge, and hence the number of parts to be junked together with other components is largely reduced. Therefore, it is possible to obtain a structure which is preferable and economical from both the viewpoints of saving of resources and the cost. In the case where the belt cartridge is of the recycling type, the structure of the belt cartridge is simplified so that works of recycling and checking require little time period and man power.
In order to attain the other object, the invention provides an image forming apparatus in which a belt is singly attachable to and detachable from the plural belt support rolls, wherein at least one of the plural rolls is a tension roller in which a rotation shaft is movable in a direction along which predetermined tension is applied to the belt, a main unit of the image forming apparatus comprises a belt tension applying mechanism which moves the tension roller to apply the predetermined tension to the belt, and in attachment of the belt, the belt tension applying mechanism is engaged with the rotation shaft of the tension roller to apply the predetermined tension to the belt.
Also, in the invention, the belt tension applying mechanism which moves the tension roller to apply predetermined tension to the belt is disposed on the side of the main unit of the image forming apparatus. Therefore, mechanism in a region enclosed by the belt has a simplified structure, whereby cumbersome in checking of the mechanism in the narrow region can be eliminated.
In order to attain the further object, in both the above-mentioned image forming apparatuses, the apparatus comprises: a meandering detecting sensor for the belt; and a belt meandering correcting mechanism which, based on a detection result of the meandering detecting sensor, drives the belt tension applying mechanism to correct meandering.
When the meandering detecting sensor and the belt meandering correcting mechanism are provided in this way, meandering of the belt can be automatically corrected in a sufficient manner even when the degree of meandering is changed during operation or the ability of correcting meandering becomes in sufficient owing to deterioration with time.
The belt may be either of a photosensitive belt, an intermediate transfer belt, and a transfer medium transport belt.